The present invention relates to the field of video image processing, and in particular to an apparatus and a method for motion-vector-aided interpolation of a pixel of an intermediate image of an image sequence.
As known, intermediate image interpolation is required for example in the generation of a 100 Hz image sequence for visualization in a television set from a received 50 Hz image sequence, or in the generation of a slow-motion sequence in which a plurality of intermediate images are generated in temporal succession between two input images. In order to correctly reproduce motion processes in intermediate image interpolation, it is sufficiently well known to use motion vectors in intermediate image interpolation, one method for estimating such motion vectors is described for example in U.S. Pat. No. 5,386,248.
For better comprehension, the essential procedure for intermediate image interpolation using a motion vector is explained below with reference to FIG. 1.
FIG. 1 shows schematically a first image and a second image A1, A2 of an input image sequence, which are present in temporal succession and to which there is generated an interpolated intermediate image A12 that, in correspondence to the input images A1, A2, has a plurality of pixels of which one pixel Px is schematically illustrated in FIG. 1. Assigned to this pixel is at least one motion vector vec1, which is generated on the basis of the input image sequence. The generation of the motion vector is based on the fact that a moving object B is located at a first position in the first input image A1 at the time of the first input image, and “shifts” to a second position in the second input image A2 by the time the second input image is “photographed”. The motion vector vec1 contains the motion information of this object. Along with the motion vector vec1, the position of the object after the motion is depicted in the input image A1 and the position of the object before the motion is depicted in the input image A2 for clarification. Using the motion vector vec1 and the video information value P0 at the initial point of the vector vec1 in the image A1, or the video information value P1 at the final point of the motion vector vec1 in the image A2, and with allowance for the raster position of the intermediate image A12 relative to the input images A1 and A2, the pixel Px of the intermediate image lying on the motion line of the vector vec1 can be determined.
Selecting the pixel P0 lying at the initial point of the motion vector vec1 assigned to the pixel Px in the first image or the pixel P1 lying at the final point of the motion vector vec1 in the image A2 is theoretically sufficient for the interpolation of the pixel Px.
However, the estimation of the motion vector or motion vectors, involves uncertainties. For this reason it is known to assign two motion vectors to a pixel to be interpolated, to apply median filtering to the video information item of the initial point in a first input image and the video information item of the final point in a second input image of the one motion vector as well as the average of the video information items of the initial point and the final point of the other motion vector, and to use the video information value resulting therefrom as the video information value for the pixel to be interpolated.
An object of the present invention is to furnish an improved method for motion-vector-aided intermediate image interpolation.